Question

我正在尝试监控GPIO引脚，根据Linux文档，我应该可以通过使用/sys/class/gpio/gpio##/value监控select文件来执行此操作：

"value" ... reads as either 0 (low) or 1 (high).  If the GPIO
    is configured as an output, this value may be written;
    any nonzero value is treated as high.

    If the pin can be configured as interrupt-generating interrupt
    and if it has been configured to generate interrupts (see the
    description of "edge"), you can poll(2) on that file and
    poll(2) will return whenever the interrupt was triggered. If
    you use poll(2), set the events POLLPRI and POLLERR. If you
    use select(2), set the file descriptor in exceptfds. After
    poll(2) returns, either lseek(2) to the beginning of the sysfs
    file and read the new value or close the file and re-open it

我试图在Ruby中执行此操作，并根据IO.Select documentation调用select(2)。

所以，凭借这些知识，我将以下测试程序汇总在一起：

fd = File.open("/sys/class/gpio/gpio17/value", "r")

loop do
  rs,ws,es = IO.select(nil, nil, [fd], 5)
  if es
    r = es[0]
    puts r.read(1)
  else
    puts "timeout"
  end
end

但是，它没有检测到任何引脚变化。当我启动此应用程序时，它将立即进入if块并显示引脚的当前值，然后每5秒打印一次timeout。

我是否读过错误的文档？ select不应该监控这个吗？

Answer 1

在select正确触发GPIO引脚之前，您需要设置引脚的边沿触发。来自the GPIO docs：

"edge" ... reads as either "none", "rising", "falling", or
    "both". Write these strings to select the signal edge(s)
    that will make poll(2) on the "value" file return.

    This file exists only if the pin can be configured as an
    interrupt generating input pin.

简单地在Ruby中：

File.open("/sys/class/gpio/gpio17/edge", "w") { |f| f.write("both") }

上面的完整示例如下：

fd = File.open("/sys/class/gpio/gpio17/value", "r")
File.open("/sys/class/gpio/gpio17/edge", "w") { |f| f.write("both") }

loop do
  rs,ws,es = IO.select(nil, nil, [fd], 5)
  if es
    r = es[0]
    puts r.read(1)
  else
    puts "timeout"
  end
end

选择GPIO监控

1 个答案: